This project utilizes a bona fide rat hepatocyte culture which was derived by cloning from a culture of newborn rat liver cells. Aflatoxin B1 is the carcinogen used to transform the cells. We currently have banks of cells frozen in liquid nitrogen which all derive from the cloned cell: (1) non toxin-treated cells from the point of inception of the culture to over passage 100; (2) Toxin-treated and control cells at each point in the transformationn process; (3) intrinsically transformed cells. We are examining these cultures morphologically, biochemically and karyologically in an effort to relate the transformation event to some point in the cultural history. Having the cultures available at each stage in their history and being aware of doubling the numbers which have occurred at each stage it should be possible to pinpoint the transformational event and hopefully relate it to one or more biological parameters.